Uterine leiomyomata (UL), or fibroids, are a major source of gynecologic morbidity among reproductive-aged women and account for 2.1 billion dollars in health care costs each year in the United States. Black women are 2-3 times more likely than white women to be diagnosed with UL and have more severe disease at the time of clinical presentation. Estrogen and progesterone have been implicated in the development and growth of UL. Using data from the Black Women's Health Study (BWHS), a nationwide prospective follow-up study of 59,000 African-American women, we propose to prospectively assess dietary risk factors (e.g., fiber and fat intake) that might contribute to the high incidence of clinically relevant UL in black women. We will focus on dietary factors that plausibly have an effect on sex hormone synthesis, metabolism, or bioavailability. We will investigate the influence of these dietary factors on the incidence of self-reported UL confirmed by ultrasound or surgery. Since the inception of the BWHS in 1995, women have been followed biennially by questionnaire. Food frequency questionnaires were completed by participants in 1995 and 2001. Validation studies in the BWHS have demonstrated high accuracy of self-reported UL (>96%) and satisfactory correlation of the food frequency data with dietary recalls and diaries. During follow-up from 1997-2007, over 6,000 incident cases of fibroids confirmed by ultrasound or surgery will have been reported. The large number of incident cases will provide high statistical power and allow for informative subgroup analyses, e.g. among women under age 35 (N=2,400 cases) and non-obese women (N=3,800) among whom misclassification should be minimized. The high incidence of UL in black women is a problem of public health importance. Dietary patterns hypothesized to increase risk (e.g., high fat and low fiber intake) are more prevalent in black women than white women. Thus, the proposed study will permit evaluation of modifiable risk factors that may contribute to the excess UL incidence among black women. Moreover, the study can be carried out at low cost because BWHS data collection is supported by other grants. The proposed study, led by a new investigator with extensive experience in studying risk factors for UL, would be the largest by far of diet and UL, the first prospective study, and the first study in black women. Project Narrative: Uterine leiomyomata (UL), or fibroids, are a major source of gynecologic morbidity among black women and account for 2.1 billion dollars in health care costs each year in the United States. Using data from the Black Women's Health Study (BWHS), a large prospective follow-up study of African-American women, we propose to study dietary risk factors that might contribute to the high incidence of clinically relevant UL in black women. Dietary patterns hypothesized to increase risk (e.g., high fat and low fiber intake) are more prevalent in black women than white women. Thus, the proposed study will permit the evaluation of risk factors for clinically relevant UL that may contribute to the excess incidence among black women.